1. Field of the Invention
The present invention relates to an automatic perimeter for automatically examining the field of vision of a patient's eye. More specifically, the present invention pertains to an automatic perimeter which is designed to automatically present marks or stimuli in accordance with various conditions including brightness, positions, presentation time and presentation intervals of the stimuli.
2. Description of the Prior Art
In general, a perimeter has a hemispherical concave screen on which stimuli are presented. In such perimeter, a patient's eye to be examined is located at the center of the sphere of the screen and the sight axis of the eye is fixed at the center of the screen by having the eye focus on a fixed viewing target on the screen. Then, the stimuli are presented in accordance with various conditions in sequence at various positions on the screen with different sizes and different brightness so as to distinguish visible zones from invisible zones.
Meanwhile, conventional automatic perimeters have a plurality of examination programs for stimulus presentation, for example, a screening examination program, a meridional examination program for longitudinal examination, and a glaucoma examination program. The perimeter is designed so that it reads a specific program or a first stimulus presentation program at the beginning of each examination. It has been common to have the program preliminarily determined by a manufacturer in view of the fact that it is frequently used as a first examination and the burden imposed on the operator can be decreased by preliminarily determining the program.
It should, however, be noted that problems have been encountered in that the first stimulus presentation program cannot be exchanged although there may be differences in the most frequently used programs for the first examinations among different treatments and examinations, such as the screening examination programs for group examinations, the meridional examination programs for generally ophthalmic examinations, or the glaucoma examination programs for adult disease examinations. In other words, the perimeter is designed so as to read the predetermined program is not at the beginning of examination, but the program is not at all used, so that the automatic perimeter mentioned above is inconvenient compared with the manual perimeter.
Other conventional automatic perimeters are designed so that a stimulus presentation program is adapted to present 50 through 200 stimuli and the presentation is carried out at random in accordance with the output of a random number generator in order to eliminate measuring errors resulting from the patient being able to predict the presentations of the stimuli. However, such a perimeter is disadvantageous in that the presentation cannot be suspended once it is started.
Conventionally, there has been proposed an automatic perimeter in which presentations of the stimuli can be suspended. In such a perimeter, the examination data obtained before the interruption of presentation of the stimuli are not presented at the output once the presentations of the stimuli are suspended, from the viewpoint that the stimuli are presented over the whole sphere of the screen in accordance with random numbers so that these data are considered not to be enough to obtain an accurate result of examination.
In general, patients suffer fatigue from these types of examinations and, therefore, it is preferable to have the examinations completed as quickly as possible. However, with the aforementioned types of conventional perimeters, it is impossible to have the examination terminated even when a malady of the patient's eye has been detected and further examination has become no longer necessary.
Further, there is known an automatic perimeter having a supplemental lens which is adapted to be inserted in front of the patient's eye. This type of perimeter is designed for examinations of eyes having extreme anomalies of refraction, for example, hyperopia and myopia. In this type of perimeter, inconveniences have been encountered in that the sphere in which the stimuli are presented has an angular extension which is so large that the patient cannot watch the stimuli presented on peripheral areas of the sphere through the supplemental lens. If the examination is carried out throughout the angular extension of the sphere through the supplemental lens, no examination data can be obtained in the peripheral areas since the field of vision is limited by the lens frame. In order to eliminate the problem, these types of perimeters have two stimulus presentation programs, one being a central zone program which covers the central area of the sphere where the patient can watch the stimuli through the supplemental lens, and a peripheral zone program where the stimuli are to be watched without the supplemental lens. It should however be noted that perimeter is inconvenient to use because the operator must move the supplemental lens into and out of the patient's sight axis manually, incurring a risk that the operator may even fail sometimes to operate the supplemental lens, and the operator must combine the data obtained through the two programs to make the judgment.